EV charger running off secondary fusebox

EV charger running off secondary fusebox

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Discussion

Mammasaid

Original Poster:

4,333 posts

104 months

Tuesday 13th August
quotequote all
If the main meter supply and fuse box are on one side of the house (rear) and we have a secondary fuse box fitted on the other side of the house (front) where I want to fit the EV charger.

Would it be possible to connect to the secondary fuse box rather than having the charger connection snake all the wat around from the front to the rear?

Pictures of meter, primary fuse box and secondary fuse box for reference.








phil4

1,322 posts

245 months

Tuesday 13th August
quotequote all
Yes, henley block after the meter, then tails off to the main house consumer unit, and a separate feed to a small consumer unit for the charger.

If your small fuse box on the other side comes of the house CU, then you'll need to find out the wire load used to decide if you can and want to pull 32Amps across it for 10+ hours.

Betters bet is as the start, take it direct from the incoming feed.

Mammasaid

Original Poster:

4,333 posts

104 months

Tuesday 13th August
quotequote all
The secondary fuse box was installed when the house was built running under the floor, it was originally added so that if we wanted to develop the outbuilding there would be sufficient power.

The alternative of running from the main fuse box is really a no starter due to the geography and the fact it was have to run outside of our property.

To give you more idea, green box is meter and main fuse box, blue box is secondary fuse box and where we'd like the charger. Red indicates property boundaries.


Krikkit

27,000 posts

188 months

Tuesday 13th August
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I suspect an electrician would want to replace the outside fusebox, swap the inside to the RCD'd side (maybe even add its own busbar so it wouldn't trip your house sockets), then you could run something more suitable outside in the secondary fusebox and have a charger hooked.

Wagonwheel555

868 posts

63 months

Wednesday 14th August
quotequote all
Assuming the outbuilding one is fed from the 32A breaker on the house CU labelled ‘Garage’?

It’s going to depend on the cable feeding the outbuilding CU and the total load.

Our EV charger has a 40a RCBO coming off the main board so I would be surprised if an electrician was happy to fit a new circuit off the outbuilding sharing the same cable and 32a upstream breaker as the sockets and lighting etc.

I’m not a sparky so it’s just an opinion, you need to get a sparky to come in and advise really. They will check and tell you within 5 minutes

tegwin

1,647 posts

213 months

Wednesday 14th August
quotequote all
Youre going to have to open up one of the consumer units and tell us what size the wire is between the two CUs.
The size will tell us what its current capacity is.

Without that information your question can not be answered.

Mr Pointy

11,859 posts

166 months

Wednesday 14th August
quotequote all
As said above the key issues are where the second CU is fed from (is it the from the 32A 'Garage' breaker in the main CU) & the size of the cable feeding it. A 7.4kW charger pulls about 31A so you can see that a 32A circuit is unlikley to be adequate.

On the bright side it look like you have a 100A incoming fuse so that is less likley to need upgrading.

Mammasaid

Original Poster:

4,333 posts

104 months

Wednesday 14th August
quotequote all
Well, I've opened up the secondary unit, and the main feeds are ~ 6-7mm each, and yes from the garage circuit on the main CU.

(I did isolate it 1st, no sparky-sparky, death-death for me today!)


ashenfie

846 posts

53 months

Wednesday 14th August
quotequote all
The cable would most likely have 4mm conductor cables and does not look to have armorer . All looks like the wiring is rather suspect.


Edited by ashenfie on Wednesday 14th August 13:02

No ideas for a name

2,408 posts

93 months

Wednesday 14th August
quotequote all
Mammasaid said:
Well, I've opened up the secondary unit, and the main feeds are ~ 6-7mm each, and yes from the garage circuit on the main CU.

(I did isolate it 1st, no sparky-sparky, death-death for me today!)

The cables look to be about 7mm outer diameter... so possibly around 4mm conductor diameter, which makes them around 12mm squared (which isn't a normal size - so the 'guess' must be wrong). Most likely they are 10mm sq by best estimation.
I can't see a problem that they aren't armoured - assuming they are protected in some other way.

Potentially (no pun), depending on length, you may be okay with that.
However - you need to KNOW the cable size, not go by my guess.

But, as already mentioned, the quality of that install is a bit suspect. Lack of ferrules and loose strands would be a worry. Trivial to fix though.
I would upgrade that DB with a metal clad one, with RCBOs.

I would be looking to see what condition the incoming tails are, and the condition of the wiring from the MCB that feeds that sub-main.

NOTE: Only take the lid off the main CU if you know what you are doing.
DON'T stick a metal tape in there to do any measurements as it looks like you don't have an upstream isolator.

IANAE


Mammasaid

Original Poster:

4,333 posts

104 months

Wednesday 14th August
quotequote all
Thanks both, I'd agree that the installation isn't the neatest.

As I said, the main cables are around 6mm in diameter, but I know for a fact that the cable back to the main CU is in a duct.

I've no intention of opening anything else, I'm not a sparky, I'm far too grounded for that! biggrin

Mr Pointy

11,859 posts

166 months

Wednesday 14th August
quotequote all
Mammasaid said:
Thanks both, I'd agree that the installation isn't the neatest.

As I said, the main cables are around 6mm in diameter, but I know for a fact that the cable back to the main CU is in a duct.

I've no intention of opening anything else, I'm not a sparky, I'm far too grounded for that! biggrin
I'd say there's a chance that incoming cable is 10mm in which case you might be lucky & be able to upgrade the 32A MCB in the main CU to 40A to give you enough headroom to run a 7.4kW charger.

I suggest you need to get an electrician who has EV charger experience to have a look & tell you what is possible, but I wouldn't be surprised if he wants to upgrade both CUs which will get spendy. Given that the garage is a separate building there might be earthing considerations as well.

Wagonwheel555

868 posts

63 months

Friday 16th August
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If it’s a 10mm cable you might be ok, the fact it’s not armoured is not the end of the world as long as it’s protected well, as mentioned already above.

However the CU in the garage doesn’t look great, personally I would get it replaced with a new one at the same time.

Just call a sparky round and ask their advice, get a three quotes and go from there.



ashenfie

846 posts

53 months

Thursday 22nd August
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Yes thats the way to go, get a sparky and he could install something like a Zappi which already has RCD and PEN. Cant imagine him wanting to touch the old 2nd cu as he would struggle to get a MCB (one that could be certified).